In general, a lithographic printing plate is composed of an oleophilic image area accepting ink and a hydrophilic non-image area accepting dampening water in the process of printing. Lithographic printing is a printing method which comprises rendering the oleophilic image area of the lithographic printing plate to an ink-receptive area and the hydrophilic non-image area thereof to a dampening water-receptive area (ink unreceptive area), thereby making a difference in adherence of ink on the surface of the lithographic printing plate, and depositing the ink only to the image area by utilizing the nature of water and printing ink to repel with each other, and then transferring the ink to a printing material, for example, paper.
In order to produce the lithographic printing plate, a lithographic printing plate precursor (PS plate) comprising a hydrophilic support having provided thereon an oleophilic photosensitive resin layer (photosensitive layer or image-recording layer) has heretofore been broadly used. Ordinarily, the lithographic printing plate is obtained by conducting plate making according to a method of exposing the lithographic printing plate precursor through an original, for example, a lith film, and then removing the unnecessary portion of the image-recording layer by dissolving with an alkaline developer or an organic solvent thereby revealing the hydrophilic surface of support to form the non-image area while leaving the image-recording layer for forming the image area.
Thus, in the hitherto known plate making process of lithographic printing plate precursor, after exposure, the step of removing the unnecessary portion of the image-recording layer by dissolving, for example, with a developer is required. However, in view of the environment and safety, a processing with a developer closer to a neutral range and a small amount of waste liquid are objectives to be achieved. Particularly, since disposal of waste liquid discharged accompanying the wet treatment has become a great concern throughout the field of industry in view of the consideration for global environment in recent years, the demand for the solution of the above-described problems has been increased more and more.
On the other hand, digitalized technique of electronically processing, accumulating and outputting image information using a computer has been popularized in recent years, and various new image outputting systems responding to the digitalized technique have been put into practical use. Correspondingly, attention has been drawn to a computer-to-plate (CTP) technique of carrying digitalized image information on highly converging radiation, for example, laser light and conducting scanning exposure of a lithographic printing plate precursor with the light thereby directly preparing a lithographic printing plate without using a lith film. Thus, it is one of important technical subjects to obtain a lithographic printing plate precursor adaptable to the technique described above.
As described above, the decrease in alkali concentration of developer and the simplification of processing step have been further strongly required from both aspects of the consideration for global environment and the adaptation for space saving and low running cost. However, since the development processing ordinarily comprises three steps of developing with an aqueous alkali solution having pH of 10 or more, washing of the alkali agent with a water-washing bath and then treating with a gum solution mainly comprising a hydrophilic resin as described above, an automatic developing machine per se requires a large space and problems of the environment and running cost, for example, disposal of the development waste liquid, water-washing waste liquid and gum waste liquid still remain.
In response, for instance, a developing method using an alkali solution having pH of 10 to 12.5 and containing a nonionic surfactant is proposed in JP-A 2002-91016 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) (corresponding to US2002/0092436A1). However, since the photosensitive layer containing an alkali-soluble polymer is used, there is a problem in that the development can not be performed with a solution having pH lower than the above-described range. Also, a lithographic printing plate precursor comprising a hydrophilic support having provided thereon an image-forming layer containing hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder is described in Japanese Patent 2,938,397 (corresponding to EP0770494A2). The lithographic printing plate precursor can be exposed imagewise using an infrared laser to agglomerate the hydrophobic thermoplastic polymer particles by heat thereby forming an image, and mounted on a cylinder of a printing machine to carry out on-machine development by supplying dampening water and/or ink.
Although the method of forming image by the agglomeration of fine particles only upon thermal fusion shows good on-machine development property, it has a problem in that the image strength (adhesion property to a support) is extremely weak and printing durability is insufficient.
As described above, the system including development with an alkali agent has a problem of supplying a replenisher for compensating the decrease of pH due to absorption of carbon dioxide and an apparatus therefor and of increase in the amount of waste liquid involved and a problem of the running cost of developer as well as the problem of environment.
Also, according to the development in an acidic to neutral range, ordinarily, it is difficult to ensure developing property and the components of the photosensitive layer removed once in the non-image area are difficult to be stably dispersed in the developer. As a result, the components of the photosensitive layer are precipitated in a developing bath and when running processing is carried out, a problem may occur in that the precipitates adhere as development scum on the lithographic printing plate precursor during the processing to be apt to cause image defect.